A battery which uses metallic contact bodies which form pressure cushions is disclosed in U.S. Pat. No. 4 317 864. The contact bodies fulfill two functions: they collect the current from each cell and they have a hollow chamber into which a pressurized medium may be introduced so that uniform compression is exerted on the catalyst material in the adjacent cells.
The electrochemical cells in such a battery are stacked one upon another in a bipolar array, with one pressure plate located at either end of the stack. Between the pressure plate and the pressure cushion of the first electrochemical cell a metal plate with an outward projecting strip is located. This plate is called the pole plate and serves as the current collection and battery connection point.
Electrical contact between the pole plate and the contact bodies (pressure cushions) is established by pressurizing the hollow chamber in the contact bodies. Either a pressurized gas or liquid can be used. However, reliable electrical contact continues only so long as the battery is operated in an atmosphere whose pressure is below that maintained in the contact bodies. If ambient pressure exceeds the pressure in the contact bodies, the current is either interrupted or the contact body, because of the loss of contact area, overloads thermally. Thus, the functional reliability of the battery is endangered.
One attempt to solve the foregoing problems consisted of gluing the pole plates into a plastic plate. The pole plate was then sealed in an elastomer frame and replaced in the battery. The space between the pole plate and the pressure cushion was thereby sealed off from the ambient pressure and changes in the ambient pressure no longer affected the contact.
That solution, however, had several disadvantages. First, gluing the pole plate into a plastic plate involved problems relating to the different coefficients of heat expansion in the materials and the dimensional changes attendant hereto. Mechanical tension caused by the gluing process and thermal stresses occurring during use generated tears and, finally, pressure leakage between the outside environment and the contact area, which impaired battery operation. Second, in order to insure the battery's functioning despite the small leaks, the space between the pole plate and the pressure cushion needed to be vented to ambient atmosphere. To maintain a relatively constant pressure within this space required costly monitoring and pressurizing equipment. Third, as multiple cells exist in each stack, the construction method was relatively costly.